Symmetry Evolution Induced Two-Dimensional Pt Single Atom Catalyst with High Density for Alkaline Hydrogen Oxidation.

The performance of single-atom catalysts is greatly influenced by the chemical environment surrounding the central atom. In this study, a salt-assisted method was employed to transform the tetrahedral coordination structure of ZIF-8 into a planar square coordination structure without altering the ligands. During the subsequent carbonization process, concurrent with the evaporation of zinc atoms, the structure of the nitrogen and carbon carriers (NC carriers) undergo a transition from five-membered rings to six-membered rings to preserve the 2D structure. Following carbonization, the 2d-NC carrier predominantly comprises pyridine N within six-membered rings, whereas the 3d-NC carrier contains a higher proportion of pyrrole N within five-membered rings, along with graphite N that unavailable for coordination sites. This transition result in the generation of additional defect sites on the 2d-NC substrates. Hence, the Pt single-atom catalysts with planar square coordination symmetries can be precisely prepared via electrodeposition (denoted as 2d-Pt SAC). By utilizing the structural characteristics of the 2d-NC carrier, it is beneficial to construct Pt SAs with higher density than that on 3d-NC. The Pt loading of 2d-Pt SAC is 0.49 ± 0.03 μg cm -2 , higher than that of 3d-Pt SAC (0.37 ± 0.04 μg cm -2 ). In the context of the hydrogen oxidation reaction (HOR) electrocatalysis, these single atom catalysts with 2d coordination exhibited exchange current densities of 1.47 mA cm -2 . Moreover, under an overpotential of 50 mV, it achieved mass activities of 2396 A g Pt -1 (32 times higher than commercial Pt/C catalyst, 2 times higher than 3d-PtNC). Our findings elucidate the influence of coordination symmetry on the performance of single-atom catalysts, offering a novel synthetic approach that may have implications for future industrial synthesis endeavors. This article is protected by copyright. All rights reserved.